Some vehicles (automobiles) are mounted with milliwave radar (referred to below as radar). Such milliwave radar is mounted to face forward on vehicle, and is used for inter-vehicle separation warning and vehicle speed control. As vehicle mounted radar, electronic scanning radars such as Frequency Modulated Continuous Wave (FMCW) radar, multi-frequency Continuous Wave (CW) radar and pulse radar are used.
When there is an obstruction around a vehicle, the vehicle mounted radar supplies target data, with relative information concerning the separation distance, orientation and velocity between the vehicle and the obstruction, to an inter-vehicle separation warning or vehicle speed control system. Inter-vehicle separation warning and vehicle speed control systems maintain a separation between the vehicle and the obstruction according to positional data of the target, issue a warning when collision is anticipated, and perform vehicle control to decelerate the vehicle (referred to below as impact reduction control) (see, for example, JP-2006-275840-A). A vehicle mounted radar is hence desired to have capability for rapidly and accurately detecting an object with which the vehicle might collide.
On general highways, there are reflective structures positioned sufficiently high above the height of the reception antenna optical axis of the radar, such as high span bridges, snow sheds and landslide shelters (referred to below as overhead objects). According to legal regulation, such overhead objects should be positioned sufficiently higher than vehicles (specifically 4.5 m or higher). Therefore, such overhead objects do not impede passage of vehicles.
However, a current radar apparatus may misdiagnose an overhead object as being an object with collision danger. Due to such a misdiagnosis by the radar apparatus, a vehicle control device will erroneously determine that there is a danger of collision, despite actually being in a safe passage state. Due to such erroneous determination, a warning may be issued or the vehicle may be decelerated unnecessarily, thereby irritating driver.
In order to address the above issue, it is attempted to control antenna directionality. However, such method requires improved high-functional. It is practically difficult to adapt antenna directionality control in vehicle mounted radars, in view of miniaturization and lower cost.
On the other hand, where there are no obstructions around the vehicle, the radar does not detect anything, and the radar does not output target data to a vehicle speed control system. In such cases, the vehicle speed control system and steering control system perform control such that the vehicle travels at the pre-set speed and steering angle.
Here, if there is an obstruction around the vehicle, sometimes, the height of the obstruction may be sufficiently low with respect to the vehicle ground clearance. Since such obstruction (referred to below as a low height object) does not impede passage of the vehicle, such obstruction should be disregarded such that there is no inter-vehicle separation warning issued, and the vehicle speed control system and the steering control system allow the vehicle to continue traveling at the already set speed and steering angle.
However, when vehicle mounted radars without resolution in the height direction is used, sometimes, the low height object may be misdiagnosed as a passage impeding obstruction depending on the antenna characteristics and the refection intensity. Due to such a misdiagnosis of the radar, a vehicle control device will erroneously determine that there is a danger of collision, despite actually being in a safe passage state. Due to such erroneous determination, a warning may be issued or the vehicle may be decelerated unnecessarily, thereby irritating driver. Further, there is a risk of being collided into by the vehicle behind.